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A man or woman who develops deep vein thrombosis, or DVT, might look like this: They're over the age of 60, have a history of smoking, had recent surgery or a leg injury, and have been immobile for some time. Each of these factors are risks for developing the blood clots of DVT. But this condition does not only affect people after 60.

When a person under age 45 develops the blood clots of DVT, the reason may be found in their genes. In about half of all young patients with DVT, a family member has also had the condition. If your mother or father has experienced DVT, you have a significant chance of having it.

However, this doesn’t mean that a person who is confined to bed and develops DVT doesn’t have a genetic condition as well. Research is finding that, in some cases, even very slight changes in genes can put a person at greater risk for DVT. Still, that inclination is generally helped by environmental conditions, such as being confined to a bed. Other factors that can contribute to DVT include being pregnant, taking birth control pills or hormone replacement therapy, and obesity.

Genetic Risks for DVT

Certain hereditary diseases increase DVT risk, including:

Protein C deficiency. A protein-C gene abnormality, a rare hereditary disease affecting only about 0.2 percent of the general population, increases the likelihood of severe blood clotting throughout the body and can be a life-threatening condition.

Protein S deficiency. This deficiency causes an abnormal interaction with other molecules in the blood, thus preventing proper coagulation. Studies show a correlation between protein-S deficiency and DVT but scientists and physicians are still researching their exact link. Doctors do not know how prevalent this deficiency is, but among Caucasians who have had DVT, between 1 percent and 5 percent were found to have a protein-S deficiency.

Antithrombin III deficiency. Between .02 percent and 1.1 percent of the population has this deficiency. Antithrombin III is a protein that normally controls coagulation. Of those who have had DVT, 4 percent were found to have antithrombin III deficiency, which can be controlled with anticoagulation medications.

A person with any of these deficiencies has a much greater risk of developing DVT if he or she inherited the faulty gene from both parents.

DVT and Factor V Leiden

Together, protein C and S deficiencies and antithrombin III comprise between 5 percent and 10 percent of all DVT cases. Factor V Leiden is responsible for many more, between 20 percent and 40 percent. About 3 percent of the general population has this gene alteration, also called a mutation. Essentially, factor V Leiden interferes with the body’s anticoagulation system.

If you inherited the factor V Leiden mutation from one parent, your risk of having DVT goes up sevenfold; with both parents, it goes up 80-fold. Add other factors, like pregnancy, cancer, or recent surgery, and it goes up even further.

DVT: Genetic Screening

If you have a first-degree relative — mom, dad, or sibling — who has developed DVT under the age of 45, you need to be tested.

"Genetic testing is available for patients at an increased risk for gene abnormalities,” says says Suresh Vedantham, MD, associate professor, department of radiology, Washington University School of Medicine in St. Louis. “This gives doctors a sense of who is at a higher risk of developing DVT. Doctors and their patients can then become better prepared for future surgeries, which can increase the chances of developing DVT."

Screening Tests for DVT

Blood tests can determine whether there is an above-average level of clotting in a person's blood. For example, the activated protein-C resistance test looks for the factor V Leiden alteration. Other tests check for protein C and S levels. But there are also genetic tests that can look for the specific mutations mentioned above and can detect very slight alterations in a person’s genetic makeup that would cause such problems.

Screening tests can help identify individuals and families who are at increased risk for future DVT episodes. With this knowledge, people can change the risk factors they have control over, like stopping smoking and making sure not to stay in one position for too long. For women, this may also mean avoiding oral contraceptives and hormone replacement therapy which increase risks of DVT. And, if a hospital stay is necessary and medical staff are alerted to the patient’s DVT risk, they can take steps to make sure a blood clot doesn’t occur.

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